Method of manufacturing sintered metallic magnets



United States Patent U.S. Cl. 148-102 3 Claims ABSTRACT OF THE DISCLOSURE A method of manufacturing sintered metal magnets which comprises compressing powders of metal and alloy consisting essentially of the base composition of 30 to 94% of Co, up to 26% of Al, and an efiective amount up to 69% total of at least one member selected from the group consisting of up to 50% Ni, up to of Ti, up to 20% of Mo, up to 13% of Cr, up to 1 8% of V, up to of W, up to 7.5% of Fe, up to 12% of Mn, up to 47% of Cu, up to 19% of Si, up to 45% of Sn, and up to 21% of Sb, to a required shape, sintering the shaped article thus obtained in a nonoxidizing atmosphere, then subjecting the article to a heat treatment for precipitating ferromagnetic fine particles of g phase in a matrix of e phase, and finally magnetizing it in a strong magnetic field.

The present invention relates to a method of manufacturing permanent magnets by sintering a mixture of powders of metals and alloys consisting essentially of to 94% by weight of Co, up to 26% by weight of Al, and up to 69% by weight of the total of at least one member selected from the group consisting of up to 50% Ni, up to 20% Ti, up to 20% Mo, up to 13% Cr, up to 18% V, up to 25% W, up to 7.5% Fe, up to 12% Mn, up to 47% Cu, up to 19% Si, up to 45% Sn, and up to 21% Sb.

The principal object of the invention is to provide homogeneous permanent magnets having large coercive force economically.

According to the invention made by the inventors it has been known that alloys made by adding one or more of 0 to 50% Ni, 0 to 20% Ti, 0 to 20% Mo, 0 to 13% Cr, 0 to 18% V, 0 to 25% W, O to 7.5% Fe, O to 12% Mn, 0 to 47% Cu, 0 to 19% Si, 0 to 45% Sn and 0 to 21% Sb in an amount of less than 69% in total to binary alloy containing 75 to 90% Co and 10 .to 25 Al, and also alloys containing 30 to 94% Co and less than 26% Al and made by melting process, if subjected to proper heat treatment give a large coercive force such as 1650 oe. at the highest. On the other hand, in point of actual application, when an article of a large size is desired to be manufactured, it may be manufactured at a comparatively low cost by casting it into a mold having a required shape and size or by forging or rolling the ingot to a desired shape and size, but when it is desired to make an article having a small size and complicated shape the above described process takes a substantial cost of manufacturing.

Hereupon the inventors have made further investigations to manufacture the above mentioned alloys by means of powder, metallurgy and invented as a result 3,519,502 Patented July 7, 1970 an excellent permanent magnet can be manufactured more easily than the case of melting process. That is, according to the invention, powders of metal or binary alloy containing 30 to Co and less than 25 Al, added with further one or more of Ni less than 50%, Ti less than 20%, Mo less than 20%, Cr less than 13%, V less than 18%, W less than 25%, Fe less than 7.5%, Mn less than 12%, Cu less than 47%, Si less than 19%, Sn less than 45 and Sb less than 21% in total amount less than 65% and some impurities are compressed and formed to a desired shape, and then sintered in vacuo, reducing or inert gas atmosphere and subjected to a suitable heat treatment to precipitate single magnetic domain fine particle of (zeta) phase in the non-magnetic matrix of e (epsilon) phase, thereby manufacturing sintered metal magnets. The metal or alloy powder to be used in carrying out said sintering process may be binary mother alloy consisting of Co-Al, Ni-Al, FeAl, or polyvalent mother alloy containing Al or mother alloy of CoAl-V, Co-AkSn, and in use of compressing powders of such alloys use is made, if necessary, of paraffin, camphor, resin or other binder or lubricant.

The term heat treatment here means such procedure that after sintering for a certain number of hours at a temperature within the range of 9 phase, the article is quenched in a quenching medium and further heated at to a temperature at least 200 C. and below the solid solubility line to precipitate single magnetic domain fine particles of 5* phase in the nonmagnetic matrix of a phase and the same efiect may also be attained by slow cooling while suitably adjusting the cooling speed after the sintering to precipitate the single magnetic domain fine particle of g phase in the nonmagnetic matrix of e phase.

Thus, subjecting the heat treatment to precipitate ferro magnetic single magnetic domain fine particle in the nonmagnetic matrix of 6 phase and then by magnetizing it in a strong magnetic field a required coercive force can be developed.

The alloys to be used for the invention contain alumimum which is easily oxidized at high temperatures, so that in order to possibly prevent oxidation of aluminum at first binary mother alloys such as Co-Al, Ni-Al and FeAl or polynary mother alloys containing aluminum, or 'Co-Al-V alloys and Co-Al-Sn alloys are made and crushed to powders of suitable size and such powders are added with deficient element in the powder form to provide as a whole a desired composition and then the mix tures are stirred thoroughly and charged into a mold having a desired shape and compressed and finally a shaped article is heated in vacuo, hydrogen stream or inert or reducing gas to sinter to provide a desired product. It, in this case, the particle of metal or alloy is small, the mixture of the powders themselves is compressed to form a desired article, but if the particle size becomes larger the shaping becomes ditficulty by alone, so that a small quantity of binder or lubricant, such as paraffin, camphor or resin is added to the mixture. The pressure when the mixture is compressed may be smaller in case of small particles, but if the size of particle is larger it requires larger pressure.

The invention will now be explained further in detail by examples.

Table 1 illustrates a comparison of characteristics of the permanent magnets made by melting an alloy of a base binary system of Co-Al added with any one of Ni, Ti, Mo, Cr. V, W, Fe, Mn, Cu, Si, Sn or Sb and characteristics of the permanent magnets made by the sintering process according to the invention.

melting and those in case of sintering, except the value 5 shows that as the concentration range of the alloys beof (BHL is a little lower in case of sintered magnet comes narrow the characteristics are more improved.

TABLE 2 Co, percent A1, percent Br (G) Hc (e) Ni, percent Ti, percent M0, percent C1, percent V, percent W, percent Fe, percent Mn, percent Cu, percent Si, percent Sn, percent Sb, percent and also the specific gravity is a little smaller in case of sintered magnet as is usual cases. In short, permanent magnets of the invention manufactured by the powder metallurgy by using an alloy added with one or more of 0 to 50% Ni, 0 to Ti, 0 to 20% Mo, 0 to 13% Cr, 0 to 18% V, 0 to W, 0 to 7.5% Fe, 0 to 12% Mn, 0 to 47% Cu, 0 to 19% Si, 0 to Sn and 0 to 21% Sb to a binary alloy of 75 to 90% Co and 10 to 25% Al and a binary alloy of 30 to 94% Co and less than 26% Al in an amount of less than 69% in total andrcontaining a small impurities can provide substantially same characteristics as those of aconventional permanent magnet manufactured by melting process and moreover, the present method has a large advantage for industrial purpose, more particularly, in the case of manufacturing magnets of a small size and having complicated shape since its cost is particularly low.

The relation between the magnetic properties and the concentration of the permanent magnets manufactured by the method of the invention is shown in Table 2. which What we claim is:

1. A method of manufacturing sintered metal magnets which comprises compressing powders of metal and alloy consisting essentially of the basic composition of 30 to 94% of Co, a substantial amount up to 26% of Al, and a substantial amount up to 69% total of at least one member selected from the group consisting of up to 50% of Ni, up to 20% of Ti, up to 20% of Mo, up to 13% of Cr, up to 18% of V, up to 25% of W, up to 7.5% of Fe, up to 12% of Mn, up to 47% of Cu, up to 19% of Si, up to 45% of Sn, and up to 21% of Sb, to a required shape, sintering the shaped article thus obtained in a non-oxidizing atmosphere, heating the article in the e+ binary region at a temperature at least 200 C. and below the solid solubility line to precipiate fine particles of ferromagnetic g in a matrix of nonmagnetic e, and finally magnetizing the product thus obtained in a strong magnetic field to obtain a magnet having high coercive force.

2. A method of manufacturing sintered metal magnets according to claim 1, wherein the alloy consists essentially of a base composition of 36 to 92.5% of Co and 1 to 24% of A1, and a substantial amount up to 62% total of at least one member selected from the group consisting up to 49% of Ni, up to 13% of Ti, up to 17% of Mo, up to 12% of Cr, up to 17.5% of V, up to 22% of W, up to 4% of Fe, up to 7% of Mn, up to 37.5% of Cu, up to 15.5% of Si, up to 37% of Sn, and up to 14% of Sb.

3. A method of manufacturing sintered metal magnets according to claim 1, wherein the alloy consists essentially of a base composition of 39 to 87% of Co and 8.5% to 20% of Al, and a substantial amount up to 52% total of at least one member selected from the group consisting of up to 46% of Ni, up to 10% of Ti, up to 12% of Mo, up to 9% of Cr, up to 13.5% of V, and up to 18% of W.

' y References Cited- UNITED STATES PATENTS 2,192,741 3/1940 Howe 148-102 2,617,723 11/1952 Studders 148-103 XR 3,203,838 8/1965 Masumoto et a1. 148-108 XR 3,211,592 10/1965 Masumoto et a1. 148-121 UJS. Cl. X.R. 148-103, 108 

